Carotenoids and tocopherol in plasma and subcutaneous fat colour to trace forage-feeding in growing steers

Abstract The aim of the study was to evaluate carotenoids and tocopherol plasma concentrations in steers and their subcutaneous fat colour at slaughter as tracers of forage-feeding. During winter, 2 groups of steers were ad libitum fed a total mixed ration for 138 days. At mid-April, both groups were turned out to graze in valley meadows and supplemented daily with 1.8 kg DM corn /head from mid-June onwards. After a grazing period of 78 days (mid-July), a group of steers remained for 75 days in the meadows until slaughter (500 kg); the second group was fed for 55 days the same total mixed ration as the one received in winter until slaughter (500 kg). The plasma concentration of carotenoids and α-tocopherol of both groups of steers during the winter and the grazing period from mid-April to mid-July was similar, reflecting the similar intake of these compounds. During the finishing period, grazing steers had greater concentrations than the steers finished on the total mixed ration. Subcutaneous fat of the steers finished on pasture had greater yellowness and chroma than the steers finished on the total mixed ration. In conclusion, it was possible to trace accurately the intake of carotenoids and tocopherols in plasma (86%), although other markers should be sought to improve traceability, and subcutaneous fat colour traits can be used to trace the diet received during the finishing period.